What radioactive sources surround you? What are their effects on your health? What does the Radiation Hormesis theory claim; Which kind of ionizing radiation is a proven carcinogen? Are there risks from the nuclear accident in Japan? How to protect yourself? How to measure the radioactivity levels in your area?
Radioactivity = ionizing radiation
Everything in nature consists of atoms. Radioactive atoms are unstable because their nuclei have a lot of energy.
During attenuation to more stable forms they emit radiation (alpha particles, beta and gamma rays) which is called ionizing because it ejects the electrons from other atoms forming ions.
Ionization activates the production of free radicals in the human body cells and may cause changes in the structure of the chromosomes of the cell membrane (mechanisms associated with cancer development).
Elevated levels of radiation can cause nausea, vomiting, burns, hair loss, infertility, impairment of the immune system and an increased incidence of certain types of cancer related death.
Especially for radioactive radon gas, which is the main source of population exposure to radiation, the World Health Organization [1] states that it is, after smoking, the second most significant cause of lung cancer (the most common cause of cancer death [2]).
Where do we receive radioactivity from?
- 55% comes from the radioactive radon gas that gushes from the earth
- 15% comes from medical applications (X-rays, scans, tumor irradiation etc.)
- 11% comes from radioactive isotopes that are naturally present in our body itself or spending through food
- 8% comes from radioactive materials in the earth's crust
- 8% comes from cosmic radiation (from the sun and space)
- 3% comes from consumer goods (fire detectors, building materials such as granite, smoking, cooking gas, etc.)
- <1% comes from nuclear plants, nuclear tests, transport of radioactive materials etc. [3]
Recent statistics from Germany show that due to the frequent mammograms, CT scans and similar medical procedures the total amount of radiation we receive from artificial sources is now equivalent to that from natural sources [4].
Where do we often record elevated radioactivity levels?
- Near building materials with high radioactive ingredients (eg. various ceramic tiles, granite counters, bricks, cement, pumice stones of volcanic ash, phosphogypsum, etc.)
- In food with radioactive residues (eg. vegetables, milk, meat and fish from the affected areas of radioactivity in Japan and neighboring regions - anything produced after March 12, 2011). In watches that glow, pottery, ionization fire detectors etc.
- In kitchens that run on natural gas
- In water from wells
- Near nuclear power plants and reactors, especially after a nuclear accident (for which the public may be informed too late, as was the case in the 1986 accident of Chernobyl).
- In the waste industries, hospitals (nuclear medicine applications), etc.
- In areas with very high altitude (higher levels of cosmic radiation)
- In areas with higher levels of radon, thorium, uranium, etc. in the underground
- In caves, hot springs and mines
- In radiodiagnostic laboratories
- In plants for cements, aluminum and phosphate fertilizers, oil drilling, power plants burning lignite, etc.
- In airplanes during flight
How real is the risk of a nuclear accident today?
Nuclear accidents are not uncommon.
So far there have been more than 152 radioactive leakage incidents recorded in nuclear plants, industrial plants, nuclear tests, etc. [5]
In many cases of nuclear leaks and accidents, such as Chernobyl, the public is informed too late, resulting in there not being enough time to take precautions.
Today there are more than 438 nuclear power plants worldwide with many others under construction. You can check the nuclear facilities of each country here.
All countries using nuclear power argue that there is no risk but as Japanese nuclear specialist Hiroshe Takashi says, if the reactors were so secure they would not be built in remote areas, but in urban centers to avoid energy losses from transmission cables [6].
What factors are related to the effects of ionizing radiation?
Type of ionizing radiation
Alpha particles: particularly dangerous when ingested through eating or inhalation through the air (radon). They can easily be shielded even with a piece of paper.
Beta particles (or electron radiation): dangerous especially when ingested through eating or inhalation through the air. They can be shielded with a metal foil (e.g. aluminum).
Gamma rays: electromagnetic radiation emitted during radioactive decay (along with alpha and beta radiation) - they have high penetration and can travel several meters in the air. They can be shielded with thick cement, lead, steel etc. They are a big part of terrestrial radiation and, along with radon gas concentrations, they are the most important for building biology assessments.
X rays: very high frequency electromagnetic radiation generated when a strong electron beam bombards a metal inside a glass tube, which is generated mainly by artificial sources in medical diagnostics etc - they have high penetration and can travel several meters in the air. They can be shielded with thick cement, lead, steel etc.
Neutron radiation: high energy unstable elementary particles with no charge - they can be obtained only from sources that produce them freshly in the atmosphere, thunderstorms, ocean etc
Cosmic radiation: Mainly gamma rays but also neutrons, can be found especially several hundred meters above sea level.
Indoor VS Outdoor exposure
Scientists often do not distinguish between the external dose of radiation that we receive internally when we inhale or consume radioactive material.
This is misleading since, as mentioned by the former secretary of the European Commission on Risk from Radiation is like comparing being warm next to the fire with swallowing hot coals! [7].
According to scientific theory, long-term exposure to very low levels of radioactivity (as a result of consumption of some radioactive elements) is a million times more harmful than the short-term outdoor exposure to high levels of radioactivity (Petkau Effect) and is likely to be associated with the development cancer and other diseases. [8]
Attenuation time
A characteristic of many radioactive materials is the long half-life ie. the time required for a radioactive element to lose 50% of its energy. These materials remain radioactive for millions of years.
However, radioactive elements with long half-life (eg. 700 million years uranium-235) have very slow decay rate subjecting us to negligible radioactivity compared to that obtained from nature or our own body (eg . Our potassium-40 in the body has a half life of 1.4 billion years).
Unlike radioactive elements with much shorter half-lives (usually released into the atmosphere from nuclear accidents), which emit more radiation in a shorter period particularly and affect the cells of specific organs.
For example, radioactive iodine-131 (8 days half-life) is mainly accumulated in the thyroid and prolonged consumption can cause thyroid malfunction and / or cancer.
Respectively, cesium-137 radioactive element (which accumulates in muscles and fat) and strontium-90 (which accumulates in bones) have about 30 years half-life and when consumed they significantly affect our cells for decades (strontium -97 is associated with leukemia).
Radiation dose
The most common unit of measurement of radioactivity is the effective dose Sievert (Sv-Sivert) depending on the type of radiation (a, b, c, X, etc.) and the amount of radiation absorbed by the human body. Another radiation dose unit used is the rem (PEM) where 1 rem = 0,01 Sv.
For many, a more reliable way of predicting possible health effects is to measure the rate of effective dose in mSv / h (micro sivert per hour).
High radiation dose values retained for longer are obviously more dangerous for humans.
A typical example are high levels of radiation following a nuclear accident which can be retained in an area for years.
What are the health effects of radiation exposure?
The Scientific Committee of the United Nations on the Effects of Atomic Radiation (UNSCEAR) [9] explainsthe mechanism responsible for ionizing radiation in detail:
"When radiation passes through material, it causes ionization which can damage chemical structures. If the material in question is biological material (such as the cells that make up human organs and tissues) and if the damage occurs to critical chemicals within the cells (such as the DNA molecules making up the chromosomes within the cell nucleus), the cell itself can be damaged.
It should be noted that the cell and the DNA are undergoing physical and chemical damage all the time (e.g. from temperature fluctuations and oxidation processes). However the cell and DNA have mechanisms to repair damage. The radiation damage will usually be repaired by these normal cell repair processes; or the cell may be sacrificed. This is of no significance if the repair is successful or if the number of cells killed is not large.
However it is possible also that the DNA may be misrepaired; in the majority of cases, such mutated cells will also die. However there is a small possibility that the cell survives and the mutation in the DNA is replicated as the cell divides. This can be the start of a multi-step process that could eventually lead to formation of a cancer.
These various possible effects at the molecular, cellular and tissue level influence the overall outcome of a person exposed to radiation. The severity of any immediate effect will depend on the total amount of exposure to radiation within a given period of time-termed the radiation dose.
If a person is exposed to very high levels of radiation for a significant period of time and the accumulated dose is high, a large number of cells can be killed. This represents serious injury to the exposed person (e.g. skin burns, hair loss, sterility, damage to the blood-producing systems and the immune system). Depending on the dose, the exposed person can recover from the injuries, particularly if good medical treatment is made available quickly. But at very high doses, recovery is not possible, leading to death over days or weeks.
At lower doses of radiation, below the levels associated with early onset of injury and death due to cell-killing, an exposed population may show an increased incidence of certain types of cancer, years to decades later, compared with populations that were not exposed. In this respect ionizing radiation is a carcinogen similar to cigarette smoke and the incidence of cancer in a population increases with the radiation dose received. In scientific studies on animals, hereditary effects have been observed, but this has never been observed in human populations, though we can assume that it probably does occur in humans to a small degree."
How do we measure radioactivity and what are the safe levels of exposure? What happens during pregnancy?
Most radioactivity meters record the rate effective dose of radioactivity, usually measured in mSv / h (micro sievert per hour).
Normal radioactivity values in the environment are generally <0.3 mSv / h (eg 0.13 mSv / h is the average global exposure to natural sources of radiation - except radon [10] and values greater than 0.4 mSv / h trigger radiation alarm in Finland).
The exposure limits set by the legislation are:
- European level occupationally exposed 10 mSv / h (20 mSv / year - 2000 working hours per year) [11]
Potential health effects depending on the radiation dose rates [12]
- 100 mSv / h: increased chance of illness
- 100 000 mSv / h: nausea, vomiting (radiation sickness)
- 1,000,000 mSv / h: increased chance of cancer
- 10,000,000 mSv / h: organ damage and death within hours
The US Nuclear Regulatory Commission (NRC) identifies high activity areas in nuclear power stations or after a nuclear accident when the readings exceed 1,000 mSv / h [13].
Multiplying the dose rate with the exposure time and you can calculate the total radiation dose in a specified period.
According to the Scientific Committee of the United Nations on the Effects of Atomic Radiation (UNSCEAR), the effects of radioactivity on humans per radiation dose are as follows:
- <10 mSv: There is no direct evidence for health effects
- 10-1000 mSv: No direct impact, increased incidence of certain types of cancer in exposed populations at higher doses
- 1000-10000 mSv: Nausea, vomiting (radiation sickness), probability of death, increased incidence of certain types of cancer in exposed populations
- > 10000 mSv: Death
Examples of radiation doses:
- 10-hour flight by plane: 0,03 mSv
- Chest X-ray: 0,05 mSv
- CT: 10 mSv
- Radon (annual report): 0,2-10 mSv (average 1,26 mSv)
- Subsoil (annual report): 0,3-1 mSv (average 0,48 mSv)
- Food (annual report): 0,2-1 mSv (average 0,29 mSv)
- Cosmic radiation (annual report): 0,3-1 mSv (average 0,39 mSv)
- Total annual radiation exposure from the natural environment: 1-13 mSv (average 2,4 mSv)
Obviously, conventional medical applications (radiography, computed tomography, scintigraphy, etc.) can considerably increase the annual radiation dose received.
Especially during pregnancy, some official scientific bodies like the Greek Atomic Energy Commission (GAEC), which is the national regulatory authority in the field of radiation safety and nuclear safety, proposes to seek alternative diagnostic methods or therapies with zero or lower radiation exposure of the fetus.
Easily measure radioactivity levels in your area with an ionizing radiation meter!
What are the health effects of radioactive radon gas?
Radon is a radioactive gas which comes from the decay of uranium found in the earth's crust and is still the major source of human exposure to radioactivity.
Radon is released from the soil and enters buildings via pipes and cracks and accumulates in low floors with inadequate ventilation. The current practice of using air-tight doors and windows for thermal insulation purposes increases the concentration of radon in modern homes.
Many areas have elevated levels due subsoil radon.
Elevated radon values are recorded near high or medium voltage cables. Research at the University of Bristol showed that the presence of high levels of low-frequency radiation increases the accumulation of radon particles in space by up to 18 times[15].
Radon is used therapeutically in dozens of spas or radon caves as well as thermal springs around the world, where patients are exposed to very high concentrations of radon for a limited time. However, long-term exposure to higher than normal levels, for example as a result of the entry of radon from cracks and pipes in homes is a possible damaging factor for humans.
Radon has been added to list of the proven carcinogens (Group 1 human carcinogen) by the International Agency for Research on Cancer (IARC - International Agency for Research on Cancer) since 1988 and according to the World Health Organization [16]:
- Radon is, after smoking, the second most common cause of lung cancer in many countries.
- Causes of between 3% and 14% of all lung cancers.
- It is the leading cause of lung cancer in non-smokers.
- The lower the concentration of radon in a home, the lower the risk.
- There is no threshold below which radon exposure carries no risk.
- The likelihood of lung cancer increases by 16% for each 100 Bq / m3 increase in the concentration of radon!
In the European Union, lung cancer is the most common cause (about 20%) of cancer related death [17].
Based on epidemiological investigations in nine EU countries it was estimated that approximately 9% of deaths from lung cancer may be due to exposure to radon in the home.
How do we measure radon, what are the safe levels of exposure and how do I reduce radon levels in my living space?
The measurement of radioactive radon gas is made with digital radon meters, detectors or dosimeters (alpha particle meters) which record the radon concentration per cubic meter (in Bq / m3). Becquerel (Bq) is the number of radioactive disintegrations per second. Another radon measurement unit used is the pCi / lt (pico-curies per liter), where 37 Bq / m3 = 1 pCi / lt.
The average radon concentration values differ from region to region and are higher indoors eg. in the USA the average values are 15 Bq / m3 outdoors and 50 Bq / m3 indoors [18].
Some officially recommended limits for exposure to radon are:
- European Union [19] (proposed for existing buildings): 400 Bq / m3
- European Union (recommended for new buildings): 200 Bq / m3
- US Environmental Protection Agency (EPA): 150 Bq / m3
- German Institute for Building Biology (IBN = Institut für Baubiologie + Ökologie Neubeuern): patient <30 Bq / m3, very strong> 200 Bq / m3
Easily measure radon levels in your area with a radon monitor!
Ways to reduce elevated radon values:
1.Increase ventilation by opening windows
2.Locate the cracks in walls, pipes and floors and seal them
3.If you are in the construction phase you can add special sealing membranes or create vacuum or a special subfloor beneath the basement floor
What are the health effects of nuclear accidents?
Near nuclear accident areas exposure to very high levels of radiation can cause nausea, vomiting, cataracts, sterility, hair loss and in some cases death [20], [21].
High levels of radioactivity due to an accident can be present in an area for years.
Radioisotopes released in nuclear accidents pollute the air and end up in vegetables and drinking water and from there get transferred to animals, milk and humans.
Nuclear accidents release radioactive elements into the atmosphere with short half-times, which emit more radiation in a shorter period and affect the cells of specific organs in particular (eg. radioactive iodine-131, cesium-137, strontium-90, etc.) .
However, estimates of scientists about the effects on health from various nuclear accidents are quite different, with the most important example being the nuclear accident at Chernobyl in 1986 [22]. Some scientists argue that the accident caused a large increase in cancers (especially thyroid leukemias), genetic deformities and early childhood mortality and considers the associated deaths approaching one million, a figure that will continually grow [23].
On the other hand, the Scientific Committee of the United Nations on the Effects of Atomic Energy (UNSCEAR) in a recent review scientific data claims that, apart from the 57 deaths that resulted from the initial explosion, the radioactive leak lead to only 4000 cases of thyroid cancer [24]. Note that the lack of iodine in the diet of the inhabitants of these areas has been an additional factor in development of thyroid cancer. [25] Also, in evacuation areas, unemployment and financial problems that followed the accident psychologically affected a large proportion of the population, which in itself had negative health effects.
How large was the nuclear accident of Fukushima compared to that of Chernobyl?
In the scale of risk of nuclear accidents, the accident at Chernobyl which was considered the biggest so far, was Grade 7. The accident in Fukushima was initially characterized a degree 4 and was upgraded to grade 7 (communication of the International Agency for Nuclear Energy on April 12, 2011 [26]).
In Chernobyl an explosion had occurred and the smoke from the fire was carrying large amounts of radioactive material across Europe for about 10 days, significantly contaminating water and food.
In Fukushima the air pollution is gradual which can exceed the total of Chernobyl, since there is far more nuclear fuel (1760 tonnes compared with only 180) and the radioactive leak can continue for decades [27].The major leak of radioactivity at present is polluting the sea and affecting the fish and seaweed.
Is there a risk for remote countries because of the radiation leakage coming from nuclear reactors in Japan?
For remote countries the problem is not so much the increase in radioactivity in the atmosphere, but the increased consumption of radioactive elements through the food chain.
The French Committee for Research and Information on Radioactivity (CRIIRAD), which measures the levels of radioactive elements in a report says that it is logical to avoid certain foods, especially for children and pregnant women, as it can not be predicted how long the radioactive contamination of the food chain will continue.
Ways of reducing exposure to radiation from a nuclear accident
- Avoid consumption of vegetables, meat, fish and milk from the affected radiation areas.
- The largest concentrations of radioisotopes are present in leafy vegetables (eg. lettuce, spinach, cabbage, etc.), except those produced in greenhouses.
- Wash vegetables before consumption (although the French Committee for Research and Information on Radioactivity claims that this practice is not very effective).
- Also radioisotopes are concentrated particularly in milk, cream and cheese from grazing animals which feed on grass (most burdened sheep).
- Use a water filter (eg. coal) for the water you drink.
- Taking potassium iodide is only recommended before or just after exposure to high levels of radioactivity. Iodine only protects the thyroid, preventing the absorption of radioactive iodine.
- Do not start taking iodine just in case, because this can also have negative effects on health. Be sure to cover the daily needs of iodine through food (natural sources of iodine: seafood, cheese, etc.). For someone who has a lack of iodine in the diet it may make sense taking seaweed supplements (eg. Kelp) which contains iodine but at lower dosages.
- Vitamin supplements and minerals that contain amounts of non-radioactive forms of cesium and strontium may offer some protection.
- Other supplements recommended are NAC (N-Acetyl-Cysteine), chlorella, spirulina, pectin etc.
- Stay indoors with windows closed or use a special mask to filter radioactive particles if you live near the accident area.
Is radioactivity always harmful?
As explained above, the effects on human health from every form of radiation depend on many factors such as type of radiation, the active radiation dose, the effective dose rate, the exposure time, whether the exposure is internal or external but also the time decay of each radioactive element.
Since man was always exposed to ionizing radiation from the natural radioactive environment , the human organism has developed some adaptation mechanisms to cope.
As mentioned by the Scientific Committee of the United Nations for the Effects of Atomic Radiation (UNSCEAR) "The radiation damage will usually be repaired by these normal cell repair processes".
Some scientists claim that damage to the cells caused by ionizing radiation, when it occurs in a controlled fashion, can enhance the body just as it happens during physical exercise. It is no coincidence that exposure to certain types of radioactivity was deliberately used for centuries for therapeutic purposes.
Radiation hormesis = a little radiation is good!
Supporters of the hormesis theory argue that radioactivity may have a health boosting effect. According to the Hormesis theory (from the Greek word Horme = rapid motion), the negative effects of toxic substances, radiation etc. are not linearly proportional to the levels of exposure. Specific doses are beneficial for the body as they cause the stimulation of all the body's systems for the repair of temporary damage. Specifically, periodic exposure to small or medium doses of radioactivity (Radiation hormesis):
- Causes controlled DNA damage that stimulates the immune system and repair mechanisms of genetic material [29].
- Regenerates cells, activates important enzymes aiding in the regulation of stress and suppresses cancer, hypertension and diabetes [30].
- Is an exercise for the immune system. "It's like doing push ups" says nuclear engineering professor at the University of Massachusetts Gilbert Brown [31].
- It dramatically improves the survival rates of animals exposed to high levels of radiation [32]. Similarly, residents of naturally radioactive areas have half of the chromosomal aberrations compared to others when they receive a high radiation dose [33].
- It is essential for the normal functioning of the body, such as vitamins and minerals, according to researcher Dr. Luckey [34]. He believes that modern man with little contact with the sun and nature suffers from lack of radioactivity.
- It was widespread in the early 20th century in the medical community. The American Medical Association had promoted the use of radioactive radium in various treatments. Radium water was sold as elixir for health [35].
- It is used to treat various symptoms by placing radioactive rocks on various parts of the body (also sold online [36]!).
- It is used as an alternative treatment for cancer, when applied to the whole body. It has an enhancing effect on the body [37], in contrast to the higher intensity ionizing radiation used topically in conventional radiotherapy which may have many side effects.
- It is used to treat arthritis [38], asthma [39] and a multitude of other diseases [40] in dozens of radon spas and radon thermal springs worldwide.
- Radioactivity levels in the healing radon spas can be very elevated - eg. in Montana, USA It is 400 times greater than the recommended limit by the US Environmental Protection Agency (EPA) [41]!
Does only ionizing radiation affect health?
The usual separation of electromagnetic radiation and non-ionizing, creates the false impression that the only biologically harmful process is ionization and that non-ionizing electromagnetic radiation from power supply, mobile phone antennas, cordless phones, WiFi, etc. is not harmful.
However, unlike radioactive ionizing radiations which has always existed in the evolution of mankind, non-ionizing radiation is mostly artificial and recently introduced to the environment. According to scientists even very low levels of exposure to non-ionizing radiation may in the long term cause significant health effects through several biological mechanisms other than ionization.
Read more about the effects of non-ionizing radiation..
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2. Radon Prevention and Remediation (RADPAR) funded from the European Commission DG SANCO Second Public Health Programme
3. Roger Eckhardt, Ionizing Radiation, Los Alamos Science, Number 23
4. Radiation Exposure, average in Germany, http://www.euronuclear.org/info/encyclopedia/r/radiation-exposure-ger.htm
5. UNSCEAR 2008 REPORT: VOLUME I, page 15
6. Hirose Takashi, What They're Covering Up at Fukushima
7. Chris Busby, Deconstructing Nuclear Experts
8. John W. Apsley, II, MD (E), DC, Radiation Toxicity Antidotes, www.doctorapsley.com
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11.Kanonismoi Radiation Protection, OG / w / 216 / 6.3.2001 (whole body exposure)
12. http://www.gavinshoebridge.com/news/basic-guide-to-radiation-levels-in-%C2%B5svh-and-msvh/
13. Wikipedia, Orders of magnitude (radiation)
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16. World Health Organization, Radon and cancer
17. Radon Prevention and Remediation (RADPAR) funded from the European Commission DG SANCO Second Public Health Programme
18. US Environmental Protection Agency, A Citizen's Guide to Radon https://www.epa.gov/radon/citizens-guide-radon-guide-protecting-yourself-and-your-family-radon
19. European Commission (EC) (reference by Radon Legislation and National Guidelines, Swedish Radiation Protection Institute)
20. Acute Radiation Syndrome, Wikipedia
21. http://depletedcranium.com/putting-radiation-exposure-in-context/
22. Chernobyl disaster, Wikipedia
23. Alexey V. Yablokov, Vassily B. Nesterenko, Alexey V. Nesterenko, Chernobyl: Consequences of The Catastrophe for People and The Environment
24. The Chernobyl accident, UNSCEAR's assessments of the radiation effects, www.unscear.org/unscear/en/chernobyl.html#Conclusions
25. Tom Bethell, Underdosed - Could toxins and Radiation be food for you ?, The American Spectator, July-August 2002
26. http://www.iaea.org/newscenter/news/tsunamiupdate01.html
27. Fukushima radioactive fallout nears Chernobyl levels, http://www.newscientist.com/article/dn20285-fukushima-radioactive-fallout-nears-chernobyl-levels.html
28. http://www.eeae.gr/gr/index.php?menu=2&fvar=html/president/_ana_anakoinosi_05_04_2011
29. Feinendegen LE. Evidence for beneficial low level radiation effects and radiation hormesis
30. Resolving the Controversy over the Beneficial Effects of Ionizing Radiation, J. Cuttler, Conference on the Effects of Low and Very Low Doses of Ionizing Radiation, World Council of Nuclear Workers
31. Matthew Shaffer, Another 3 Mile Island
32. Biology and Medicine, Interview with Dr. Sadao Hattori, the 21st st Cantury Science & Technology
33. Ghiassi-nejad et al, VERY HIGH BACKGROUND RADIATION AREAS OF RAMSAR, IRAN: PRELIMINARY BIOLOGICAL STUDIES, Health Physics January 2002, Volume 82, Number 1
34. J. Muckerheide, It's Time to tell The Truth about helath The Benefits of Low - Dose Radiation, 21 st Cantury Science & Technology, Summer 2000
35. J. Cuttler, M. Pollycove, Can Cancer be treated with Low Doses of Radiation ?, Journal of American Physicians and Surgeons, Volume 8, No 4, Winter 2003
36. www.nighthawkminerals.com
37. J. Cuttler, M. Pollycove, Can Cancer be treated with Low Doses of Radiation ?, Journal of American Physicians and Surgeons, Volume 8, No 4, Winter 2003
38. Albrecht Falkenbach et al, Radon therapy for the treatment of rheumatic diseases-review and meta-analysis of controlled clinical trials, Rheumatology International Volume 25, Number 3
39. Mitsunobu F. et al, Elevation of antioxidant enzymes in the clinical effects of radon and thermal therapy for bronchial asthma, J. Radiat. Res., 44, 95-99 (2003)
40. Neda T. et al, Radon concentration levels in dry CO2 emanations from Harghita Băi, Romania, used for curative purposes, Journal of Radioanalytical and Nuclear Chemistry Volume 277, Number 3
41. Tom Bethell, Underdosed - Could toxins and Radiation be food for you ?, The American Spectator, July-August 2002
42. Photo radon entry to house from The South Carolina Institute for Energy Studies, State Indoor Radon Program, http://www.clemson.edu/scies/RadonProgram.htm